Antenna, transmitter and coupling arrangement



G. WELCH June 20, 1961 ANTENNA, TRANSMITTER AND COUPLING ARRANGEMENT Filed Oct. 50, 1959 IHH INVENTOR GLENN WELCH ATTORNEY United States Patent 1 2,989,626 ANTENNA, TRANSMITTER AND COUPLING ARRANGEMENT Glenn Welch, 52 Highland Place, Indian Head, Md. Filed Oct. 30, 1959, Ser. No. 850,001 4 Claims. (Cl. 250-17) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates in general to a transmitter and in particular to one for transmitting widely spaced frequencies on a single antenna.

In the field of communications, it is frequently desired to transmit a selected one of a plurality of widely spaced frequencies. One arrangement in the prior art accomplishes this end by switching the driver and the output tank's and/or the antenna coupling unit in a transmitter while another employs separate transmitters for each frequency and switches a common antenna from one transmitter to another. The former arrangement lacks the necessary degree of reliability in such applications as a radiosonde system and the latter exceeds the weight and space requirements in many systems. Further, these and other arrangements in the prior art require complicated tuning circuits for simulating free space operation on the ground.

Accordingly, it is an object of the present invention to provide means for transmitting one of a plurality of widely spaced frequencies with minimum component switching.

Another object is to provide means for transmitting a selected one of a plurality of widely spaced frequencies with a single antenna and without requiring component switching, other than crystals.

Another object is to provide a transmitter that may be easily tuned on the ground for transmission in free space.

These objects are achieved by placing the resistance of the transmitter antenna across the tank circuit of the output tube during low frequency transmission and in the tank during high frequency transmission.

In one embodiment for transmitting two frequencies, the total length of the antenna is selected as a submultiple of the low frequency wavelength and the feed point is positioned off-center to present a desired resistive load at the low frequency. A wave trap, tuned to the high frequency, is positioned in the center of the antenna so that the antenna appears to be center-fed and has an impedance of 72 ohms at the high frequency. The tank circuit of the output tube includes a low frequency coil in series with a high frequency coil connected across a tuning capacitor to ground. The antenna is connected across the low frequency coil and ground so that, when the high frequency is transmitted, an antenna resistance of 72 ohms is connected in parallel with and shunts the low frequency coil. The antenna resistance is in effect in the tank circuit and in series with the high frequency coil. Since the tank circuit impedance matches the plate resistance of the output tube, maximum power is transferred to the antenna. When the low frequency is transmitted, the impedance of the high frequency coil is negligible and the antenna is connected across the plate of the output tube. Since the plate resistance is selected to be the same as that of the antenna, maximum power transfer occurs.

In the figures:

FIG. 1 is an embodiment of the present invention.

FIG. 2 is equivalent circuit of the antenna and output electron tube plate circuit at high frequencies.

FIG. 3 is an equivalent circuit of the antenna and output electron tube plate circuit at low frequencies.

2,989,626. Patented June 20, 1961 ICC ' Referring to 'FIG. 1, source of DC. potential 10 is connected across motor 12, which drives clock 13. As minute hand 14 sweeps segment 15, a circuit is completed from source of DO. potential 16 through relay Ryl to ground. -As the minute hand sweeps segment 17, a similar circuit is completed through relay RyZ to ground.

Armatures Ryl-l, Ry2-2 and tRy31 are shown in the positions assumed when their associated relays Ry1, Ry2, Ry3, respectively, are denergized. When relay RyZ is unenergized crystal 18, in parallel with capacitor 19, is connected between the control grid of electron tube 20 and ground. When the relay is energized armature RyZ-l is placed in a lower position in FIG. 1 grounding source of DC. potential 16 through relay Ryl. Likewise, armature Ry2-2 is moved to the lower position placing crystal 24, which is connected in parallel with capacitor 25, between the control grid of electron tube 20 and ground. Resistor 21 is also connected between the control :grid and ground and capacitors 26, 27 form a series circuit between the same two points. Choke 28 and resistor 29 are connected in series between the cathode of electron tube 20 and ground, The cathode is connected to a point located between capacitors 26, 27, the screen grid of the electron tube is connected through capacitor 30 to ground, and the suppressor grid directly to the filament.

Parameter sensor 32 includes one or more conventional devices selected to provide signals in dependency upon parameters such as temperature and humidity. These signals are applied to signal generator 33 which in turn develops signals in Morse code, for example, or controlling switch 34.

When relay Ryl is energized, armature Ryl-l engages the contact to the left in FIG. 1 completing a series circuit from source of DC. potential 16 through the filaments of electron tubes 20, 35 to ground. When switch 34 is closed a circuit is completed from the source of DC. potential through relay Ry3 to ground. Capacitor 36 is placed across relay Ry3 to prevent sparking when the relay is keyed.

Capacitor 38, low frequency tank circuit 39, and high frequency tank circuit 40 form a series circuit positioned between ground and the plate of electron tube 20. The low frequency tank comprises coil 41 in parallel with capacitors 42., 43, while the high frequency tank comprises coil 44in parallel with capacitor 45. Capacitor 46 is located between the plate of electron tube 20 and the control grid of electron tube 35. The control grid of electron tube 35 is connected to ground through choke 47, resistor 48, sourceof DC. potential 49 and jack 50 in such a manner that the source of DC. potential applies a fixed negative bias to the control grid of the electron tube. Capacitor 51 is connected between the filament of electron tube 35 and a point between source of DC. potential 48 and choke 47.

When relay Ry3 is energized, armature Ry3-1 is placed in the lower position in FIG. 1 and establishes a circuit from terminal 55, resistor 56 and choke 57 to the screen grid of electron tube 35. The positive potential on terminal 55 is also applied through resistor 59, tank circuits 39, 40 to the plate of electron tube 20 and through resistor 60 to the screen grid of the electron tube. The screen grid of electron tube 35 is connected to the filament through capacitor 58.

Variable condenser 64 is connected between the plate of electron tube 35 and ground while high frequency coil 65 is connected in series with capacitor 66 between the plate of the electron tube and terminal 67 of antenna 68. The high frequency coil, low frequency tuning coil 70, and capacitor 71 are connected in series between the plate of the electron tube and ground. Terminal 72 on antenna 68 is grounded. Wave trap 74 includes coil 75 connected across the series circuit comprising coil 76 and capacitor 77. The wave trap is located a selected distance from the lower end of antenna 68 in FIG. 1 that is determined by the magnitude of high frequency to be transmitted. The value of the low frequency to be transmitted and 5 the plate resistance of electron tube 35 determines the location of terminals 67, 72 on the antenna. Terminal 55 is connected through choke 78 to a point located between low frequency tuning coil 70 and capacitor 71.

The following table sets forth electron tubes and values of resistors, capacitors, chokes, etc., which have been found satisfactory in the operation of the embodiment in FIG. 1 for a low frequency of 6700.5 kc. and a high frequency of 18013.5 kc. It should be understood that the table and frequencies are exemplary only and at not to be interpreted in a limiting sense.

Potential on terminal 55 350 volts. Source of DC. potential 10 3 volts. Source of DC. potential 16 6 volts. 20 Source of DC. potential 49 1.5 volts. Electron tube 20 6AK6. Electron tube 35 2E24. Clock 13 6 volt D.C. clock. Crystal 18 6700.5 kc. Crystal 24- 9006.75 kc. Capacitors 19, 25 5-25. Capacitors 26, 46 l0. Capacitor 27 62. Capacitors 30, 51, 58, 38 1500. 30 Capacitor 36 0.5 1f. Capacitor 42 120. Capacitor 43 7-45. Capacitor 45 3-12. Capacitor 64 5-15. Capacitors 66, 71 750. Capacitor 77 15. Resistor 21 47K. Resistor 29 360 ohms. Resistors 48, 56 18K. Resistor 59 4K. Resistor 60 110K. Chokes 28, 47, 57 750 ,uh. Choke 78 l mh. Wave trap 18013.5 kc. trap. Antenna lengths A, B, and C 12'6", 13 and 48'3",

respectively.

Note: the value of all capacitors are given in micro- 5o microfarads unless indicated otherwise.

In aligning the disclosed embodiment, antenna 68 is disconnected from terminals 67, 72 and a suitable ammeter is inserted in jack 50. Armature Ry2-2 is positioned as shown in FIG. 1 and capacitor 43 are adjusted for maximum current in the grid circuit of electron tube 35. This aligns the circuits associated with electron tube 20 for operation on the low frequency. Because the low frequency is so far below the resonance of high frequency tank circuit 43, the latter has an inductive reactance and tank circuit 39 is tuned to the low frequency. Armature Ry2-2 is then placed in the lower position shown in FIG. 1 and capacitor 45 is set for maximum ammeter current so that the plate and grid circuits of electron tube 20 are adjusted for operation on the high frequency. On this frequency tank circuit 39 appears to be a low capacitive reactance grounding one side of high frequency tank circuit 40. In adjusting the plate circuit of electron tube 35 for operation on the high frequency, terminals 67, 72 are shorted and capacitor 64 is positioned for minimum plate current dip; and for operation on the low frequency, the shunt is removed and low frequency tuning coil 70 is set for minimum plate current dip.

In the operation of the embodiment, when minute hand 14 engages segment 17, relay Ry2 is energized and arma- 75 tures Ry2-1, Ry2-2 move to the lower position in FIG. 1. Crystal 24 is connected to the grid circuit of electron tube 20 so that the high frequency is generated. Because of the position of wave trap 74, antenna 68 functions at the high frequency as a half wave dipole having a resistance which has a value of 72 ohms and is positioned across coils 69, 70. Since the coils are selected to have an impedance of approximately 2000 ohms during high frequency operation, the equivalent circuit, as shown in FIG. 2, includes the 72 ohm resistance located in series with coil 65. The entire tank current flows through the antenna providing maximum power transfer to the same.

When minute hand 14 senses segment 15, only relay Ryl is energized. Armature Ry2-2, therefore, remains in the position shown in FIG. 1. Crystal 18 is connected in the grid circuit of electron tube 20 and the low frequency is generated. At this frequency, wave trap 74 is ineffective, the impedance of high frequency coil 65 may be neglected, and the entire length of antenna 68 is used. Since terminals 67, 72 are selectably positioned 15 electrical degrees off-center, the antenna resistance at the low frequency is approximately 4000 ohms and, as shown in the equivalent circuit in FIG. 3, the resistance of the antenna 81 is located across plate resistance r,,. Since the antenna and plate resistances are substantially equal, maximum power is transferred to the antenna.

During either high or low frequency operation, armature Ryl-l is positioned to the left in FIG. 1 and signal generator 33, controlled by parameter sensor 32, provides signals that operate switch 34. As the switch is operated, the screen grid of the output tube 35 is keyed to modulate the transmitted frequency in dependency upon the magnitude of selected parameters.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In an arrangement for transmitting at least a first frequency having a selected wavelength and a second fre quency having a second wavelength, an output circuit including an electron tube with a selected plate resistance and having at least a plate, filament and control grid, a tank circuit including a first coil and a second coil connected in series between the plate of said electron tube and ground, an antenna having an electrical length substantially equal to half the wavelength of said first frequency, a wave trap positioned from one end of said antenna by an electrical distance substantially equal to half said second wavelength, said wave trap being tuned to said second frequency, a first input terminal and a second input terminal positioned off the electrical center of said antenna by a distance such that said antenna has a resistance when operated on said first frequency substantially equal to said plate resistance, a third terminal positioned between said first and second coils, and means for connecting said first input terminal to ground and said second input terminal to said third terminal.

2. In an arrangement for transmitting at least a first frequency and a second frequency, said second frequency having a wavelength substantially less than the wavelength of said first frequency, an output circuit having a selected resistive impedance, a tank circuit connected to said output circuit, said tank circuit comprising a capacitive section and an inductive section connected in parallel and across said resistive impedance of said output circuit, said inductive section including at least a first portion and a second portion connected in series, the impedance values of the sections of said tuned circuit being such that said capacitive section and said first and second portions of said inductive section define a resonant circuit at said first frequency and said capacitive section and said first portion of said inductive section define a resonant circuit at said second frequency, an antenna having an electrical length substantially equal to one half the wavelength at said first frequency, said antenna including a wave trap tuned to said second frequency and disposed with respect to one end of said antenna at a distance substantially equal to one half the wavelength at said second frequency, said antenna having an input substantially at the midpoint between said wave trap and said one end of said antenna such that said antenna is operative as a center fed antenna at said second frequency, and means connecting said antenna input across said second portion of said inductive section in said tuned circuit.

3. The arrangement as defined in claim 2 wherein said output circuit is an electron tube and said resistive impedance is the plate resistance thereof.

4. The arrangement as defined in claim 3 wherein said first and second frequencies are in such relation that the wavelength at said second frequency is less than one half the wavelength at said first frequency.

References Cited in the file of this patent UNITED STATES PATENTS 2,267,445 Cork et al. e Dec. 23, 1941 2,505,781 Mallinson May 2, 1950 2,898,590 Pichitino Aug. 4, 1959 

